The major objectives of this contract will be to (1) maintain a repository for the production, maintenance, and distribution of aneuploid mice with primary emphasis on trisomy 16 and (2) develop improved mouse models of chromosomal disorders, again with emphasis on trisomy 16. Two aspects of the project will be (1) to test which Robertsonian combinations are best for producing whole chromosome trisomies of specific chromosomes and (2) to induce translocations with small marker chromosomes containing segments of Chr. 16 and other selected chromosomes and demonstrate that adult mice with trisomy for small segments of the genome can be produced.